Polymer–Carbon Black Composite Sensors in an Electronic Nose for Air-Quality Monitoring

ArticleinMRS Bulletin 29(10):714-9 · November 2004with30 Reads
DOI: 10.1557/mrs2004.208 · Source: PubMed
Abstract
An electronic nose that uses an array of 32 polymer-carbon black composite sensors has been developed, trained, and tested. By selecting a variety of chemical functionalities in the polymers used to make sensors, it is possible to construct an array capable of identifying and quantifying a broad range of target compounds, such as alcohols and aromatics, and distinguishing isomers and enantiomers (mirror-image isomers). A model of the interaction between target molecules and the polymer-carbon black composite sensors is under development to aid in selecting the array members and to enable identification of compounds with responses not stored in the analysis library.
    • "S INCE their advent, conductive polymer matrix composites (CPMCs) have proved to be functional materials for electronic applications owing to some favorable properties [1]. These materials are prepared by dispersing conducting particles in an inherently insulating polymer and are widely used in embedded capacitors [2], memory devices [3], pressure sensors [4], temperature sensors [5], current limiting devices [6], electromagnetic interference shielding and microwave absorption layers [7], and humidity and chemical sensors [8]. CPMC-based devices offer several advantages in comparison with their inorganic rivals, including easy and low-temperature processing, printability over large areas, simple device structures, optical transparency, and lightweight and mechanical flexibility [3], [9]. "
    [Show abstract] [Hide abstract] ABSTRACT: A comprehensive study is conducted on the electron transport in conductive polymer matrix composites (CPMCs), employing the nonequilibrium Green’s function formalism. This paper provides a microscopic insight into the electron tunneling through the potential barriers existing between conducting sites. It is shown that Wentzel–Kramers–Brillouin approximation as well as other models with simple barrier shapes, which are widely used in literature, can lead to inaccurate results in comparison with the quantum mechanical approach using a hyperbolic barrier. In this paper, unlike most previous ones, percolation-related effects are disregarded for further focus on electron transport through the polymer potential barriers. It is assumed that a tunneling-conductive channel exists between the electrodes. This can be created either by applying electric field alignment or using a filler volume fraction higher than the percolation threshold. A two electrode resistive device is studied and the results indicate that a conductor–insulator transition occurs at a barrier thickness of $sim 1.7$ nm and the barrier thickness should be larger than several angstroms. Next, a novel tunneling field-effect structure based on CPMCs is introduced and its characteristics are comprehensively investigated. This device features a remarkably simple structure, an extremely high channel to gate coupling, a large transconductance, and a high current level. Besides, it has the advantage of being based on polymers. This ensures favorable physical properties, ease of fabrication, and low-cost processing techniques.
    Full-text · Article · May 2015
    • "Nevertheless, Ryan et al. showed an increase in R/R o when PCL-carbon black composite was exposed to SO 2 , a reducing gas [47]. Carbon black is widely used as a conductive medium without specific sensing functionality and relays electrical signals detected by insulating polymers in an electronic nose [48] . In this setup, SO 2 interacts with the ester linkage , reacting with the carbonyl functional groups by donating its electron [49]. "
    [Show abstract] [Hide abstract] ABSTRACT: Electrospinning provides a means to synthesize nanofibrous structures with very high surface area-to-volume ratio, which enhance the sensitivity of conductive polymer (CP)-based gas sensors in a cost effective manner. To enhance processability, insulating host polymers are often used with the CP for electrospinning. Unlike CPs, however, the contribution of insulating polymers on overall sensing performance of composites has not been systemically investigated. In this study, we examined the effects of insulating polymers in electrospun composite nanofibers on the sensitivity to various analytes. Different composition ratios of polyaniline (PANI)/poly(ɛ-caprolactone) (PCL) nanofibers were produced by electrospinning, and their structure and chemistry were characterized. The PANI/PCL electrospun composite nanofibers were configured in a chemiresistor and subjected to different analytes, including H2O vapor, NH3, and NO2. H2O vapor and NO2 showed a polarity change in sensitivity, having a compositional threshold of PANI-to-PCL ratio. To investigate this polarity change, the temperature dependence of electrical conductivity was examined. When H2O vapor was exposed to the composite with the highest PANI content at 20 wt%, there was a decrease in hopping distance; on the other hand, an increase in hopping distance was observed when H2O vapor was exposed to the composite with the lowest PANI content at 9 wt%. These results show an existence of competition between the conductive polymer, PANI, and the insulating host polymer, PCL, for analyte interaction, both of which integratively determine the overall sensitivity. The work demonstrates that the host polymer plays an important role in structural swelling as well as chemical interaction with analytes, which critically modulate sensing behavior.
    Full-text · Article · Feb 2015
    • "Therefore, the importance of detecting the presence of VOCs in indoor air goes beyond health concerns. Over the last few decades, many sensors have been designed to detect VOCs, such as surface acoustic wave sensors [8,9], polymer composite sensors101112 carbon nanotubes131415, CMOS [16], and capacitive sensors [17]. Information about VOCs may be provided by colorimetric sensor array technology. "
    [Show abstract] [Hide abstract] ABSTRACT: In this paper, we propose a volatile organic compound (VOC) gas sensing system with high sensitivity and a wide dynamic range that is based on the principle of the heterodyne frequency modulation method. According to this method, the time period of the sensing signal shift when Nile Red containing a VOC-sensitive membrane of a fiber-optic sensing element comes into contact with a VOC. This sensing membrane produces strong, fast and reversible signals when exposed to VOC gases. The response and recovery times of the proposed sensing system were less than 35 s, and good reproducibility and accuracy were obtained.
    Full-text · Article · Dec 2014
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